automatic 2 gear jackshaft

dmopedMA

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Apr 14, 2017
Messages
171
UPDATE (May 5):
I decided to update this first post pointing to the, I believe, milestones of this project:

First schema:

Custom made long shaft:

When I realized that only one shaft won't be enough to hold the second clutch:

First gearbox prototype:

First test of the gearbox, didn't engage the second gear:

Second prototype of the gearbox enclosure (thicket aluminium):

First test of the second prototype with weaker springs on the clutch:


ORIGINAL POST:
I'm working on a non-pedal chopper (https://motoredbikes.com/threads/4-stroke-schwinn-stingray-chopper-occ.51001/), the motor is a 49cc HS 4-stroke with the 4G transmission, using a 40t on the back wheel it gets 30mph.

I'm thinking on how to make it quicker and at the same time legal in MA, so if I use gears they have to be automatic (MA moped law)... I would love to have 2 gears, one for quick start from stop (right now it's not as quick as I would like) and other to get to 30mph (max speed by law). A classic jackshaft with bike gears won't be legal in MA and my bike does not have bike gears now.

I got an idea from go-karts using a second centrifugal clutch on a jackshaft, here a link with something similar: http://www.rcdon.com/html/grv-1_turbotug_project_12_01_0.html. From the 4G transmission I'll put two identical puller sprockets (10t) going to the jackshaft, on the jackshaft two sprockets, one big for the first gear and other small for the second gear (specific sizes to be determined), both connected with a chain to the correspondent 4g sprocket. The first gear will have a free-wheel, so it makes the jackshaft spin but not the other way around. The second gear will have a centrifugal clutch, so it will freely spin in low jackshaft RPMs and will engage the second gear when the jackshaft get close to the high rpms of the first gear. To make it clear, in low RPMs, the second gear will spin free (and faster) over the jackshaft that will be driven by the first gear and when the second speed engages, the freewheel of the first one will allow it to spin slower than the jackshaft. The output of the jackshaft will be connected to the back wheel on the right side.

Does anyone tried something like that before??? is this kind of system for sale?

EDIT: I just found a schema of the idea:

My_version_of_a_2_speed_clutch_web.jpg
 
Last edited:


DanTheDIYGuy

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Jun 21, 2016
Messages
83
I would think it would be easier and more practical to use a belt-driven centrifugal clutch automatic transmission on the jackshaft. The higher the RPM's, the more the belt moves up on a conical shaped pulley. This would increase speed on level ground, and increase torque on hills based on how the engine's RPM's vary.
 

dmopedMA

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Apr 14, 2017
Messages
171
I would think it would be easier and more practical to use a belt-driven centrifugal clutch automatic transmission on the jackshaft. The higher the RPM's, the more the belt moves up on a conical shaped pulley. This would increase speed on level ground, and increase torque on hills based on how the engine's RPM's vary.
I'm not sure about it, as far as I know there is no torque converter that is compatible with the small HS motor (49cc), just let me know if I'm wrong.
 

dmopedMA

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Apr 14, 2017
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171
I was doing some math tonight and from the 4G I already have a reduction of 4:1, meaning that It's going to be almost impossible to engage a regular HS centrifugal clutch (3000 RPMs to engage) on the jackshaft unless I seepd up to reduce it later... I researched a little bit and looks like there are "low RPM" centrifugal clutches that engages from 600RPM with different combinations up to 3000RPM, so I may need one that engage around 1600RPM to engage when the motor is over 6500RPM.

I have to draw a new diagram, moving the second clutch to the 4G output instead of the jackshat and I feel this is not for sale as I need it... all the ones I see that are already made are design to run instead of the 4G transmission and on go-karts or minibikes...

If the price of the components is not crazy I may try to build it myself.
 

curtisfox

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May 13, 2010
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620
Mopeds them self have a auto transmission, with a 50 cc engine. Not sure how they work, haven’t had one apart yet .....Curt
 

dmopedMA

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Apr 14, 2017
Messages
171
Mopeds them self have a auto transmission, with a 50 cc engine. Not sure how they work, haven’t had one apart yet .....Curt
They use CVTs which I believe there is no one designed for the HS 49cc motor (as far as I know)
 

dmopedMA

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Apr 14, 2017
Messages
171
Here is a sketch of the idea:
IMG_20180628_124904.jpg



Motor is on top and wheel on bottom.

The 20T-80T is the 4G transmission I already have, the second bar will be the jackshaft. I'll need an extended shaft for the 4G to accommodate the second gear clutch (low RPM)
 

curtisfox

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May 13, 2010
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620
Thought so but never had one apart yet, designed for 50 cc. msrfan on motorbicycling forum built one, used one way needle bearing, search and see if you can find it, nice compact.......Curt
 
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